1. Field of the Invention
The present invention relates to a chemical vapor deposition apparatus and a method of manufacturing a semiconductor device, and more specifically, to a chemical vapor deposition (CVD) apparatus for forming a dielectric film applied to a semiconductor memory device and a method of manufacturing a semiconductor device using the chemical vapor deposition apparatus.
2. Description of the Background Art
In recent years, increasingly higher degree of integration is being achieved in semiconductor memories and semiconductor devices at a great speed. For instance, a dynamic random access memory ()RAM) has undergone a rapid increase in the bit number: it has quadrupled in three years. The aims are to achieve higher degree of integration of the device, lower power consumption, lower cost, and so on. A capacitor, which is a component of a DRAM, however, is required to have a constant capacitance regardless of the improved degree of integration of the device.
One way of ensuring the capacitance of a capacitor is to create a thin capacitor insulating film. With the silicon oxide film (SiO2) that has been used until now, however, there are limits as to how thin the film could be formed.
Consequently, as another way of ensuring the capacitance of a capacitor, the material for the capacitor insulating film has been changed. In other words, a thin film formed of a material having a high dielectric constant came to be utilized as the capacitor insulating film.
Oxide-type dielectric films as examples of high dielectric constant materials including, for instance, tantalum oxide, lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), strontium titanate (ST), barium titanate (BT), barium strontium titanate ([(Ba, Sr)TiO3] hereinafter referred to as xe2x80x9cBSTxe2x80x9d), and the like are being considered.
In order to form such oxide-type dielectric film as a thin film on a capacitor electrode of a DRAM having steps, it is advantageous to employ the CVD method which provides favorable coating onto a surface having a complex shape. In CVD method, a liquid source is used as a source for the thin film having a high dielectric constant. The liquid source is prepared by dissolving an organometallic complex containing a certain metal in an organic solvent. The liquid source is vaporized, and the resultant vapor is blown against the substrate to form a thin film having a high dielectric constant.
A significant problem has been, however, that a liquid source having a stable and good vaporization characteristic does not exist. This is mainly due to the poor vaporization characteristic, upon heating, of the compound of a metal and xcex2-diketon-type dipivaloyl methane (DPM) frequently used as an organometallic complex.
Under these circumstances, the present inventors proposed a CVD source having a greatly improved vaporization characteristic by utilizing a liquid source prepared by dissolving a conventional organometallic complex in an organic solvent called tetrahydrofuran (THF: C4H3O) (Japanese Patent Laying-Open No. 7-268634).
It was discovered, however, that a dielectric film having a good quality such as a good electrical property could not always be consistently formed when the film was formed with this CVD source using a conventional CVD apparatus for liquid source. Thus, the present inventors proposed in Japanese Patent Laying-Open No. 8-186103 a CVD apparatus for liquid source which allows adequate vaporization of the liquid source and which supplies the vapor stably to the reaction chamber.
Now, the CVD apparatus for liquid source disclosed in the above Japanese Patent Laying-Open No. 8-186103 will be described with reference to the drawing. In FIG. 16, the CVD apparatus for liquid source is provided with liquid source vessels 164 to 167, liquid source flow rate control systems 160 to 163, a vaporizer 156, and a reaction chamber 153. Liquid source vessels 164 to 167 each store a liquid CVD source prepared by dissolving an organic complex containing a prescribed metal in an organic solvent.
To each of the liquid source vessels 164 to 167 a pressure tube 169 is connected, and through pressure tube 169 an inert gas such as nitrogen is fed into each of the liquid source vessels 164 to 167. Consequently, the pressure inside each of the liquid source vessels 164 to 167 rises, causing the liquid CVD sources to be supplied to vaporizer 156. Here, the flow rates are respectively controlled by liquid source flow rate control systems 160 to 163. In addition, a carrier gas such as nitrogen is introduced from a carrier gas feed inlet 168 in order to send the liquid CVD source via a connecting tube 158 to vaporizer 156. Here, the flow rate is controlled by a carrier gas flow rate control system 159.
Liquid CVD source, having reached vaporizer 156, is vaporized therein, and the resultant vapor flows through a source gas conveying tube 155 to a mixer portion 170. Conveying tube heaters 157 are provided around source gas conveying tube 155 to prevent the CVD source gas from turning back into liquid. The CVD source gas and oxygen supplied from an oxidizing agent feed line 154 are mixed in mixer portion 170. The CVD source gas mixed with oxygen is introduced into reaction chamber 153 via a source gas inlet 171, and thereafter, a thin film is formed on a substrate 151.
When forming a BST film as the thin film, liquid sources prepared by respectively dissolving in an organic solvent the organometallic complexes respectively containing barium (Bi), strontium (Sr), and titanium (Ti) were used. Oxygen ambient was provided inside reaction chamber 153, and the pressure was set between 1 and 10 Torr. The temperature of a substrate heater 152 was set to be in the range of 400xc2x0 C. to 600xc2x0 C. The flow rates of the liquid sources and the film deposition time were controlled such that the value of the BST film composition ratio (Ba+Sr)/Ti was 1.0. In this case, the film deposition rate was 3 nm/min.
As described above, liquid sources prepared by dissolving the DPM-type organometallic compounds in an organic solvent were used as the CVD sources. The source gas vaporized in vaporizer 156 is introduced into reaction chamber 153 via source gas inlet 171. At this time, a substantially steady flow of source gas from source gas inlet 171 directed to exhaust outlet 172 is formed in reaction chamber 153.
As a result, there was a problem of uneven distribution within the substrate surface regarding the thickness and the composition ratio of the BST film formed on substrate 151. More specifically, the film thickness tended to be relatively thick on the side where exhaust outlet 172 was provided. As regards the film composition ratio, the film tended to contain more titanium (Ti) than barium (Ba) or strontium (Sr) nearer to the exhaust outlet.
Moreover, the attempt to rotate the substrate to eliminate the unevenness within the substrate surface caused the problem of particle generation accompanied by the rotation.
Further, in the above-described CVD apparatus for liquid source, the source gas introduced from the inlet diffused inside reaction chamber 153 so that the vapor was not effectively brought onto substrate 151, which led to the problem of a low xe2x80x9cuse efficiencyxe2x80x9d or the ratio of the amount of the source gas contributing to film growth to the amount of the source gas supplied being low.
In addition, in a conventional CVD apparatus for liquid source, some of the heat from substrate heater 152 was absorbed by a wall of reaction chamber 153 having a low temperature so that a portion having a relatively low temperature was created within reaction chamber 153, causing the source gas introduced into reaction chamber 153 to condense in that portion. As a result, the condensed source gas was attached onto the substrate 151 as particles of foreign substance.
This, moreover, lead to another problem that the source gas could not be effectively brought onto substrate 151 due to the condensing of the source gas.
The present invention was made to solve the above problems. One object of the present invention is to provide a chemical vapor deposition apparatus allowing improved evenness of film thickness and film quality such as composition ratio within the substrate surface, with the substrate being fixed in position, while suppressing the generation of particles of foreign substance within the reaction chamber and increasing the use efficiency or the ratio of the source gas that contributes to film growth. Another object of the present invention is to provide a method of manufacturing a semiconductor device using such a chemical vapor deposition apparatus.
The chemical vapor deposition apparatus according to one aspect of the present invention is provided with a reaction chamber, a fixed stage portion, a blow inlet, and exhaust outlets. The fixed stage portion holds a substrate within the reaction chamber. The blow inlet introduces the source gas into the reaction chamber. The exhaust outlets exhaust the source gas having undergone the reaction from the reaction chamber. By causing the direction of the flow of the source gas introduced into the reaction chamber to vary with time, the direction of the flow of the source gas relative to the substrate also varies with time.
According to this configuration, as the direction of the flow of the source gas relative to the substrate varies with time while the substrate is fixed in position, improved evenness of film thickness and film quality such as composition ratio within the substrate surface is achieved. In addition, as the direction of the flow of the source gas within the reaction chamber varies with time, the product of reaction is kept from being attached to particular portions in the reaction chamber and the generation of particles within the reaction chamber can be suppressed. As a consequence, the number of particles of foreign substance being attached onto the substrate is reduced.
A specific method of varying the direction of the flow of the source gas within the reaction chamber with time preferably involves varying the direction to exhaust the source gas with time.
More preferably, the exhaust outlets are provided in at least two locations in the reaction chamber, and each exhaust outlet has an open and shut mechanism portion for opening and shutting each exhaust outlet successively with time.
In this case, the direction to exhaust the source gas is varied with time by opening and shutting the open and shut mechanism portions of the exhaust outlets so that the direction of the flow of the source gas can easily be changed.
More preferably, the open and shut mechanism portion for opening and shutting the exhaust outlet includes an open and shut valve.
In this case, opening and shutting the valve can easily change the direction of the flow of the source gas.
Preferably, the open and shut mechanism portion includes a ballast gas introducing mechanism portion for supplying a ballast gas into each exhaust outlet to prevent the source gas from flowing into each exhaust outlet.
In this case, the flow of the source gas into the exhaust outlet is prevented in the exhaust outlet where the ballast gas is supplied so that the source gas flows into the exhaust outlet that does not have the ballast gas supplied into it. By successively changing the exhaust outlet to supply the ballast gas into, the exhaust outlet that exhausts the source gas changes accordingly, and thus, the direction of the flow of the source gas within the reaction chamber can be varied with time.
In addition, the open and shut mechanism portion preferably includes a rotational shutter having an opening formed thereto and allowing to exhaust the source gas through that opening as the opening crosses each of the exhaust outlets by rotation.
In this case, the exhaust outlet to exhaust the source gas can be easily changed by the rotation of the rotational shutter having an opening formed thereto so that the direction of the flow of the source gas within the reaction chamber can easily be varied with time.
More preferably, a guiding plate portion for guiding the source gas from the blow inlet toward the substrate is provided.
In this case, the source gas does not diffuse inside the reaction chamber during its travel from the blow inlet to the substrate so that the source gas can positively reach the substrate, whereby the ratio of the source gas contributing to the film growth increases.
The chemical vapor deposition apparatus according to another aspect of the present invention is provided with a reaction chamber, a stage portion, a blow inlet, and a guiding plate portion. The stage portion holds the substrate in the reaction chamber. The blow inlet introduces the source gas into the reaction chamber. The guiding plate portion guides the source gas from the blow inlet toward the substrate.
According to this configuration, the source gas does not diffuse inside the reaction chamber during its travel from the blow inlet to the substrate so that the source gas can positively reach the substrate. As a result, the ratio of the source gas contributing to film growth increases.
The guiding plate portion can preferably be heated.
In this case, the source gas leaking out of the guiding plate portion can be prevented, and the amount of the source gas being attached to an inner wall of the reaction chamber can be reduced. As a result, the ratio of the source gas contributing to film growth increases even further while the generation of particles of foreign substance within the reaction chamber is successfully suppressed.
More preferably, a purge gas introduction portion for allowing a purge gas to flow between the reaction chamber wall and the guiding plate portion is provided.
In this case, diffusion of the source gas outside the guiding plate portion is prevented, and the ratio of the source gas contributing to the film growth is improved.
More preferably, the purge gas introduction portion includes a heating portion for heating the purge gas.
In this case, transfer of heat from inside the reaction chamber to the outside can be prevented, and formation of a portion having a relatively low temperature within the reaction chamber can also be prevented. As a result, the condensing of the source gas within the reaction chamber and the generation of particles of foreign substance that accompanies the condensing of the source gas can be reduced.
The method of manufacturing a semiconductor device according to still another aspect of the present invention includes the step of having a semiconductor substrate fixedly held inside the reaction chamber, and forming a prescribed film on the semiconductor substrate while varying the direction of the flow of the source gas relative to the semiconductor substrate by varying the direction of the flow of the source gas introduced into the reaction chamber with time.
According to this manufacturing method, as the direction of the flow of the source gas varies relative to the semiconductor substrate, evenness of the thickness and the composition ratio and the like of the prescribed film within the semiconductor substrate surface is improved. In addition, since the flow of the source gas within the reaction chamber changes with time, the amount of the product of reaction that are attached to particular portions inside the reaction chamber is reduced, and the number of particles of foreign substance falling onto the semiconductor substrate also decreases.
In particular, when barium strontium titanate (13ST) film is formed as the prescribed film, improved evenness in thickness of the BST film and in the composition ratio of barium (Ba), strontium (Sr), and titanium (Ti) within the semiconductor substrate surface is achieved.
The source gas preferably is guided directly toward the semiconductor substrate.
In this case, the source gas positively reaches the semiconductor substrate so that the ratio of the source gas contributing to film growth increases.